Low power high resolution sensor interface

Abstract

A sensor interface circuit is provided for resolving sensor signals from a plurality of sensors into a digital sensor signal. The sensor interface circuit includes a relaxation oscillator that receives and pre-processes the sensor signals to generate an analog sensor signal. The relaxation oscillator includes one or more dynamic circuits. The sensor interface circuit also includes a monitoring module for receiving the analog sensor signal and generating the digital sensor signal in response thereto. There is also provided a sensor system front-end and a relaxation oscillator.

What is claimed is: 
     
       1. A sensor interface circuit for resolving sensor signals from a plurality of sensors into a digital sensor signal, the sensor interface circuit comprising:
 a relaxation oscillator for receiving and pre-processing the sensor signals to generate an analog sensor signal, the relaxation oscillator comprising one or more dynamic circuits; and 
 a monitoring module for receiving the analog sensor signal and generating the digital sensor signal in response thereto, the monitoring module comprising: 
 a fixed frequency generation device for generating a clock signal having a fixed frequency of clock pulses; and 
 a variable window frequency counting device for determining a number of clock pulses within a variable counting window. 
 
     
     
       2. The sensor interface circuit in accordance with  claim 1  wherein the variable window frequency counting device varies the variable counting window between a predetermined minimum oscillator frequency and a predetermined maximum oscillator frequency, the predetermined minimum oscillator frequency and the predetermined maximum oscillator frequency determined in response to operational parameters of the relaxation oscillator. 
     
     
       3. The sensor interface circuit in accordance with  claim 1  wherein the fixed frequency generation device has a fixed frequency determined in response to operational parameters of the relaxation oscillator. 
     
     
       4. The sensor interface circuit in accordance with  claim 1  wherein the monitoring module further comprises front end circuitry coupled between the relaxation oscillator and the variable window frequency counting device for pre-processing the analog signal from the relaxation oscillator for frequency counting by the variable window frequency counting device. 
     
     
       5. The sensor interface circuit in accordance with  claim 1  wherein the relaxation oscillator further comprises one or more comparators having a comparator reference voltage, and wherein the one or more dynamic circuits includes a dynamic capacitor circuit coupled to the comparators, the dynamic capacitor circuit being configured to reduce its discharge capacitance in response to a determination that its capacitor voltage approximates the comparator reference voltage of the one or more comparators. 
     
     
       6. The sensor interface circuit in accordance with  claim 5  wherein the dynamic capacitor circuit comprises one or more MOS varactors respectively coupled to the one or more comparators. 
     
     
       7. The sensor interface circuit in accordance with  claim 1  wherein the relaxation oscillator further comprises one or more capacitors, and wherein the one or more dynamic circuits includes a dynamic current discharge circuit coupled to the one or more capacitors, the dynamic current discharge circuit being configured to increase a discharge current for the one or more capacitors in response to a determination that a voltage of the one or more capacitors approximates a comparator reference voltage. 
     
     
       8. The sensor interface circuit in accordance with  claim 7  wherein the relaxation oscillator further comprises one or more comparators having the comparator reference voltage, and wherein the one or more dynamic circuits further includes a dynamic capacitor circuit comprising the one or more capacitors and coupled to the comparators, and wherein the dynamic current discharge circuit is configured to increase the discharge current and the dynamic capacitor circuit is configured to reduce its discharge capacitance in response to a determination that its capacitor voltage approximates the comparator reference voltage. 
     
     
       9. A sensor system front-end comprising:
 a plurality of sensors; and 
 a sensor interface for resolving sensor signals from the plurality of sensors into a digital sensor signal, the sensor interface comprising: 
 a relaxation oscillator for receiving and pre-processing the sensor signals to generate an analog sensor signal, the relaxation oscillator comprising one or more dynamic circuits; and 
 a monitoring module for receiving the analog sensor signal and generating the digital sensor signal in response thereto, wherein the monitoring module comprises: 
 a fixed frequency generation device for generating a clock signal having a fixed frequency of clock pulses; and 
 a variable window frequency counting device for determining a number of clock pulses within a variable counting window. 
 
     
     
       10. The sensor system in accordance with  claim 9  wherein the plurality of sensors comprise a plurality of resistive sensors. 
     
     
       11. The sensor system in accordance with  claim 9  wherein the plurality of sensors comprise a plurality of capacitive sensors. 
     
     
       12. The sensor system in accordance with  claim 9  wherein the variable window frequency counting device varies the variable counting window between a predetermined minimum oscillator frequency and a predetermined maximum oscillator frequency, the predetermined minimum oscillator frequency and the predetermined maximum oscillator frequency determined in response to operational parameters of the relaxation oscillator. 
     
     
       13. The sensor system in accordance with  claim 9  wherein the fixed frequency generation device has a fixed frequency determined in response to operational parameters of the relaxation oscillator, and wherein the monitoring module further comprises front end circuitry coupled between the relaxation oscillator and the variable window frequency counting device for pre-processing the analog signal from the relaxation oscillator for frequency counting by the variable window frequency counting device. 
     
     
       14. The sensor system in accordance with  claim 9  wherein the relaxation oscillator further comprises one or more comparators having a comparator reference voltage, and wherein the one or more dynamic circuits includes a dynamic capacitor circuit coupled to the comparators, the dynamic capacitor circuit being configured to reduce its discharge capacitance in response to a determination that its capacitor voltage approximates the comparator reference voltage of the one or more comparators. 
     
     
       15. The sensor system in accordance with  claim 14  wherein the dynamic capacitor circuit comprises one or more MOS varactors respectively coupled to the one or more comparators. 
     
     
       16. The sensor system in accordance with  claim 9  wherein the relaxation oscillator further comprises one or more capacitors, and wherein the one or more dynamic circuits includes a dynamic current discharge circuit coupled to the one or more capacitors, the dynamic current discharge circuit being configured to increase a discharge current for the one or more capacitors in response to a determination that a voltage of the one or more capacitors approximates a comparator reference voltage. 
     
     
       17. The sensor system in accordance with  claim 16  wherein the relaxation oscillator further comprises one or more comparators having the comparator reference voltage, and wherein the one or more dynamic circuits further includes a dynamic capacitor circuit comprising the one or more capacitors and coupled to the comparators, and wherein the dynamic current discharge circuit is configured to increase the discharge current and the dynamic capacitor circuit is configured to reduce its discharge capacitance in response to a determination that its capacitor voltage approximates the comparator reference voltage. 
     
     
       18. A relaxation oscillator comprising:
 comparators, each having a comparator reference voltage input, a signal input and an output, wherein the comparator reference voltage input of each of the comparators are connected to a comparator reference voltage source; 
 variable capacitors, wherein the number of the variable capacitors is equal to the number of the comparators, and wherein each of the variable capacitors is connected between a ground voltage potential and the signal input of a corresponding one of the comparators and each of the variable capacitors is controlled to reduce its discharging capacitance only when its capacitor voltage approximates a voltage of the comparator reference voltage source; 
 discharge circuits respectively coupled to the variable capacitors, each of the discharge circuits coupled to the respective variable capacitor is coupled to the ground voltage potential and an oscillator output, the discharge circuits are configured to increase a discharge current for the variable capacitors only when a voltage of the variable capacitors approximates the voltage of the comparator reference voltage source; 
 an oscillator input section for receiving a sensor input from a plurality of sensors and providing the sensor input to each of the signal inputs of the comparators; and 
 a frequency generation circuit coupled to the output of the comparators and to the oscillator input section for generating an analog signal from the sensor input for provision to an oscillator output of the frequency generation circuit by controlling provision of the sensor input to the signal inputs of the comparators.